# -*- coding: UTF-8 -*-  
import sys
import pygame
from bullet import Bullet
from alien import Alien

def check_keydown_events(event, ai_settings, screen, ship, bullets) :
    # 响应按键，按下事件
    if event.key == pygame.K_RIGHT:
        ship.moving_right = True
    elif event.key == pygame.K_LEFT : 
        ship.moving_left = True   
    elif event.key == pygame.K_SPACE :
        # 如果没有达到限制就创建一颗子弹并加入编组bullets
        fire_bullet(ai_settings, screen, ship, bullets)
    elif event.key == pygame.K_q :
        # 按Q 退出
        sys.exit()

def check_keyup_events(event, ship) :
    # 响应按键，弹起事件
    if event.key == pygame.K_RIGHT :
        ship.moving_right = False 
    elif event.key == pygame.K_LEFT :
        ship.moving_left = False  

def check_events(ai_settings, screen, ship, bullets) :
    # 监视键盘和鼠标事件
    
    # 响应按键和鼠标事件 
    for event in pygame.event.get():
        if event.type == pygame.QUIT :
            sys.exit()
        elif event.type == pygame.KEYDOWN :
            check_keydown_events(event, ai_settings, screen, ship, bullets)
        elif event.type == pygame.KEYUP :
            check_keyup_events(event, ship) 

def update_screen(ai_settings, screen, ship, aliens, bullets) :
    # 更新屏幕上的图像，并切换到新屏幕

    # 每次循环时都重新绘制屏幕
    screen.fill(ai_settings.bg_color)
    # 在飞船外绘制子弹
    for bullet in bullets.sprites() :
        bullet.draw_bullet()

    ship.blitme()
    aliens.draw(screen)
    # 让最近绘制的屏幕可见
    pygame.display.flip()

def  update_bullets(bullets) :
        # 更新子弹状态
        bullets.update()

        # 删除已消失的子弹
        for bullet in bullets.copy() :
            if bullet.rect.bottom <= 0 :
                bullets.remove(bullet)

def fire_bullet(ai_settings, screen, ship, bullets) :
        # 如果没有达到限制就创建一颗子弹并加入编组bullets
        if len(bullets) < ai_settings.bullets_allowed :
           new_bullet = Bullet(ai_settings, screen, ship)
           bullets.add(new_bullet)

def get_number_aliens_x(ai_settings, alien_width) :
    """计算每行可容纳多少外星人"""
    available_space_x = ai_settings.screen_width - 2 * alien_width
    number_aliens_x = int(available_space_x / (2 * alien_width))

    return number_aliens_x

def get_number_rows(ai_settings, ship_height, alien_height) :
    """计算屏幕可容纳多少行外星人"""
    available_space_y = (ai_settings.screen_height - (3 * alien_height) - ship_height)
    number_rows = int(available_space_y / (2 * alien_height))

    return number_rows

def create_alien(ai_settings, screen, aliens, alien_number, row_number) :
    """创建一个外星人并将其加入当前行"""    
    alien = Alien(ai_settings, screen)
    alien_width = alien.rect.width
    alien.x = alien_width + 2 * alien_width * alien_number
    alien.rect.x = alien.x
    alien.rect.y = alien.rect.height + 2 * alien.rect.height * row_number
    aliens.add(alien)

def create_fleet(ai_settings, screen, ship, aliens) :
    """创建外星人群"""
    # 创建一个外星人，并计算一行可容纳多少个外星人
    # 外星人间距为外星人宽度
    alien = Alien(ai_settings, screen)
    
    number_aliens_x = get_number_aliens_x(ai_settings, alien.rect.width)
    number_rows = get_number_rows(ai_settings, ship.rect.height, alien.rect.height)

    # 创建外星人群
    for row_number in range(number_rows) : 
        for alien_number in range(number_aliens_x) :
            # 创建一个外星人并将其加入当前行
            create_alien(ai_settings, screen, aliens, alien_number,row_number)